Sick Vampire Bats Socially Distance To Protect Colony

Despite their reputation, vampire bats care enough for their roost-mates to keep away when they're sick, lest they spread an infectious disease. Sherri and Brock Fenton/Behavioral Ecology

People who won't listen to scientists and health officials telling them to keep their distance during a pandemic could take lessons from vampire bats, although we're not holding our breath.

As we have been painfully reminded this year, bats are the reservoirs for many human pathogens, although just how distinctive they are in this is debated. Part of the reason is bats' sophisticated immune systems that allow them to carry, but not be seriously affected by, diseases that are lethal to us. However, work by Dr Simon Ripperger of Ohio State University suggests this is not the whole story – when bats do get sick they behave in a more socially responsible manner than many humans.

Scientists have observed that bats in captivity put some distance between themselves and healthy counterparts when sick. Ripperger and colleagues set out to test the more important question of whether this happens in the wild, but they didn't want to actually infect bats with a transmissible disease. For one thing, this would pose a threat to a colony's survival. For another, the specific infectious agent might distort the findings, such as when infection with Toxoplasma gondii makes rodents behave in ways that increase the chance of the parasite being passed on.

Instead, Ripperger's team caught 41 adult female vampire bats, releasing seven that were pregnant. Half of the rest were injected with lipopolysaccharide, a chemical that sparks an immune system response similar to many diseases. The remaining got a saline solution. All were fitted with sensors measuring their proximity to each other and had their movements described in Behavioral Ecology

All the bats shared a large hollow in a single tree; three perhaps privacy-aware beasts managed to remove their trackers but the rest revealed which other bats they hung out with and for how long. Those given the lipopolysaccharide isolated themselves in the limited roosting space and had four fewer associations that were less than 50 centimeters (20 inches) apart during a six-hour period than the healthy controls. Once the lipopolysaccharide wore off, the affected bats slowly returned to normal levels of interaction with the rest of the colony.

"The sensors gave us an amazing new window into how the social behavior of these bats changed from hour to hour and even minute to minute during the course of the day and night, even while they are hidden in the darkness of a hollow tree," Ripperger said in a statement. "We've gone from collecting data every day to every few seconds."

The authors note that the bats did not set up some sort of quarantine quarter where all the sick individuals were isolated – those given the lipopolysaccharide were even less likely to associate with each other than with healthy bats. Instead, bats that felt sick just kept to themselves, reducing the risk of transmission.

Such behavior clearly benefits the colony but doesn't necessarily the sick bat, at least directly. It seems despite their unsavory reputation, bats have worked out the value of looking after those around them by not spreading their diseases. Perhaps our Halloween outfits should all be socially distanced vampire bats.

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